The major sources of commercially mined Li2CO3 have historically come from brine solution and spodumene containing ores. To date, there has been no commercial production of Li2CO3 from lepidolite rich ores or concentrates. Lepidolite is present in many pegmatite deposits, and co-exists with spodumene in some pegmatites. The presence of lepidolite is problematic for refineries that produce Li2CO3 from spodumene concentrate. As such, the lithium content of lepidolite holds no value and is rejected at the spodumene concentrator.
There have been several efforts to recover lithium from lepidolite in the laboratory and one commercial application. Importantly, none of these prior art efforts have involved direct leaching of the mineral.
A process to extract lithium from lepidolite and produce LiOH is described in U.S. Pat. No. 2,940,820, lodged in 1958. The process was implemented by the American Potash & Chemical Co (operating as American Lithium Chemicals Co) in 1955-1960. Lepidolite was mixed with limestone at a mass ratio of 3:1 then wet ball milled. The discharge from the mill was then filtered and the filter cake was subject to roasting in a rotary kiln at 911° C. The discharge was quenched, milled and then leached in a counter-current mixer settler system. Aluminium impurities were precipitated by the addition of lime and the precipitate was removed by filtration. The filtrate was then evaporated to force the crystallization of LiOH.H2O of relatively low purity. These crystals were purified by re-crystallization to produce a saleable product. This process relies on low power and limestone costs to be viable, which significantly limits its widespread application.
U.S. Pat. No. 3,189,407 describes a process in which lithium is said to be recovered from low lithium minerals, such as lepidolite, by reaction of the mineral with sulfuric acid and lithium is ultimately precipitated from solution. In this process, lepidolite is first pulped with acid and heated to a temperature of between 140° C. and 200° C., preferably 150° C. to 170° C. (an acid bake) in what is said to be an effort to react only with the lepidolite and not the gangue that may be present. The bake is run over a period of up to 4 hours and only small levels of aluminium and potassium are said to be dissolved. Most of the water present evaporates during the bake, leaving a product substantially in the form of a thick paste, not what might typically be described as a slurry. This paste is then re-pulped in water. Aluminium is then precipitated through the addition of an alkali or alkali earth carbonate to increase the pH to between 3.5 to 4.5. The recovery process of the present disclosure has as one object thereof to substantially overcome the problems associated with the prior art or to at least provide a useful alternative thereto.
The preceding discussion of the background art is intended to facilitate an understanding of the present disclosure only. It should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was part of the common general knowledge in Australia or any other country or region as at the priority date of the application.
Throughout the specification and claims, unless the context requires otherwise, the word “comprise” or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.
Throughout the specification and claims, unless the context requires otherwise, the word “mica”, “micas” or obvious variations thereof will be understood to refer to the group of complex hydrous aluminosilicate minerals that crystallize with a sheet or plate-like structure. Specifically, the mica referred to herein is to be understood to refer to lithium containing mica.